Source of ultra violet light



06L 1, 1940. J. HANNUM 2,216,237

SOURCE 0! ULTRA VIOLET LIGHT Original Filed Sept. 28, 1933 in itsspectrum.

Patented on. l, 1940 PATENT OFFICE SOURCE OF ULTRA VIOLET LIGHT JohnAndrew Hannum, Cleveland Heights, Ohio,

alaignor to General Electric Company, a corporation of New YorkApplication September 28, 1933, Serial No. 691,396 Renewed May 13, 19384 Claims.

Ultra violet light has become of such importance and is used for so manycommercial purposes that it is highly desirable to be able to produce itat a nominal cost, and at the same time with a high intensity. At thepresent time, among its commercial uses may be listed the irradiation oimilk, cereal foods and tobacco. A rather popular use which has recentlycome into prominence is the use of ultra violet light to produceartificial sunburn on the human body.

This form of light radiation which is just short of the visible spectrumat the short wavelength end is at present produced in several ways. Thetwo best known methods are the use of the carbon arc; and a mercury arcin a quartz container.

There are two essentials demanded of ultra violet light: First, it mustcome from a powerful source; second, from an efilcient source. Twothings are meant by the term efilcient source. First, there must be amaximum of output for a given amount of electrical energy supplied;second, this output must be as free from any light other than ultra.violet as possible. In short, the object is to produce as much ultraviolet with as little input as possible.

The present lamps have several objections from the standpoint of boththe quantity of rays or light emitted, as well as the efiiciency of thelamp used to emit this light. The average ultra violet light sourceemits in addition to ultra violet, light in the visible spectrum andradiation in the infra red.

The element indium is the most outstanding of all metals in regard tothe number of lines emitted It has a far greater number of lines in theultra violet as compared with the rest of the spectrum than has anyother element. Not only is the profusion of lines greater in the ultraviolet spectrum, but the intensity of these lines is to a marked degreegreater than similar lines of any other element. Thus, it will be seenthat by making use of a source of ultra violet light comprisingessentially luminous indium as a source it will be far superior to anyknown means of producing this light. My invention, by using metallicindium, results in a light source which is both eillcient and capable ofproducing an intense light.

I use a container the walls of which will pass ultra violet light andwhich may be evacuated or filled with an inert gas. Electrodes protrudeinto this container as a. means of bringing the electrical energyrequired therein. Also in this container is a quantity of'indium eitherin the elementary state oras an alloy, amalgam or salt.

illustrates the preferred embodiment thereof.

In accomplishing these objects it is to be understood that I am notlimiting myself to the specific disclosures shown in the drawing andhereinafter 1 described.

Referring now to the drawing:

Figure l is a front elevation of my improved source of light.

Figure 2 is a sectional view as indicated by the 20 line 2--2 on Figure-1.

Figure 3 is an elevation of an end portion of a lamp using my preferredform of cooling fins.

Figure 4 is a section through this portion of the tube as indicated bythe line 4-4 on Figure 3.

Figure 5 is a side elevation of a modified form of tube which allows thecooling of the auxiliar tubes containing the electrode leads.

In Figure 1 l0 indicates the main body tube of the lamp and l i theauxiliary tubes through 30 which the electrodes are conducted to themain tube. The electrode leads i2, preferably made of tungsten, may beconnected to any suitable source of electrical energy. The tubescomprising the lamp shell are preferably made of transparent quartz.

In bringing the electrodes into the lamp it is of course necessary tohave an effective seal in order that the hermetical seal of the entiredevice may be maintained. Thus in Figure 2 the electrode 40 lead l2enters a cup or funnel-shaped portion iii of auxiliary tube H and thenpasses through the tube proper past the constriction it into the bodytube ID. The funnel-shaped portion i3 contains therein a seal of silverchloride l5 which 46 not only firmly holds the electrode lead but sealsthe tube against ingress of air.

This silver chloride is poured into the funnel in a molten state andupon hardening effects the It may happen that when this 50 requiredseal. silver chloride is poured into the funnel a small amount of itwill descend into the tube H and even flow across the horizontal portionas far as the constriction I4 before solidifying. No attempt is made toform a tight seal between the container at the constriction and theelectrode lead contained in the tube. The constriction merely serves thepurpose of causing the metallic silver chloride to be in effect dammedup and prevent it from passing the construction. The constriction alsoprevents any molten indium which may descend into the tube l6 frompassing the constriction. Thus at no time can the silver chloride or theindium come in contact either with the other.

The active agent of my invention is the indium which becomes luminousdue to electrical excitation and furnishes the principal source of theultra violet light emitted through the walls of the quartz container.This indium may be in the form of a pure element or as a salt, amalgamor alloy. Thus in the bottom portion of the arcuate body tube i0 isdeposited a quantity of indium 2U Electrode leads l 2 have projectingtips 2|, extend ing slightly into the body tube 40. I

The body tube I b is predominantly arcuate with the exception of thetube bottom 40 between the junctions of the auxiliary tubes with themain tube. This upwardly curved portion provides pockets H where theelectrode leads enter the body tube for a purpose which will behereinafter described.

One form of using indium in this lamp is as an amalgam of mercurycontaining indium. Indium in any form is deposited in the tube 10through the upwardly projecting tube 22 before this tube is sealed. Inthe case of a mercury amalgam it is desirable to place the amalgam inthe tube through a funnel sufliciently long to reach the bottom of thebody tube to prevent the tendency of the amalgam to gather on the sidesof the quartz or other material comprising the tube. The actualelectrodes in the lamp are the indium which is deposited in the pools 4iformed where the auxiliary tube containing the electrode lead enters themain body tube. When the tube is in operation the indium which may havebeen solid becomes liquid and is retained in contact with the electrodeleads it? by the sides of the pool 4!.

When the lamp is finally assembled it becomes necessary to eitherevacuate the interior or perhaps fill it with an inert gas to allow thearc to function. This evacuation takes place through the projecting tube22 which may thereafter be sealed to retain the vacuum within the tube.As heretofore mentioned, the molten indium has a tendency to adhere tothe sides of the lamp tube and short circuit the electrodes. One methodof preventing this consists of exposing the inside of the tube and theindium to a dilute solution of hydrochloric or other acid, principallyto clean the oxides from the indium. As the tube is heated as hot aspossible during evacuation the dissolved oxides volatilize oil and areremoved from the lamp interior.

Upon the complete evacuation or if desired the addition of an inert gasthe projecting tube 22 is sealed as a final step in providing anhermetically sealed quartz container for the electrodes and the indium.

If it is desired to cool a portion of the electrode encasing tubes thismay be done with a form of tube as will now be described. Referring toFigure 5, tube ll descends to form a horizontal portion 25, then isextended upwardly to form a U- shaped portion 26, and then anotherhorizontal portion 2?, after which the electrode is conducted to thebody tube ill. The upwardly facing U- shaped portion comprising parts H,25, and 26 may be inserted in a tank 30, which contains a suitablecooling fluid to surround part oi the tube.

It is usually necessary to provide a means of cooling 9, portion of theindium vapor in order to condense it. A cooling means such as indicatedin Figures 3 and 4 is preferred. Around the ends of the body tube Hi, asshown in Figure 4, are wrapped strips of metal I! which are boltedtogether with bolt 8i and nut 52. The strips ID are allowed to projectbeyond the bolt in the form of parallel strips 53. These strips may bepulled apart as indicated by 55 to increase the area through which theymay radiate heat from the body tube II.

To start the lamp it is necessary to heat the quartz container to atemperature to melt the indium therein. The tube is then rocked untilthe molten indium forms a connection between the electrodes which havebeen previously connected to a suitable source of electrical energy.This energy may be either alternating or direct current. When the moltenindium flows away from one of the electrodes the circuit is broken and aportion of this indium vaporizes and continues to carry the electricenergy from one electrode to another.

When the indium vaporizes it becomes luminous through electricalexcitation and gives of! the desired ultra violet light.

It will be seen from my disclosure that I have provided an eillclentsource of ultra violet light at a nominal cost. I provide an electricare which uses for its chief light source indium made luminous throughelectrical excitation. This indium because of the remarkable intensityof its spectrum lines and because of the profusion of these lines in therange of ultra violet light, is an admirable source of such light; bothbecause of its intensity and because of its efllciency for a givenelectrical input.

Having described my invention, I claim:

1. A source of ultra violet light comprising a crescent shaped containerwith its bottom portion arched upwardly adjacent the midsection, ahollow tube portion on each side of the midsection and leadingdownwardly therefrom and reversed upon itself to lead upwardly andterminating in an upwardly opening cup portion, an electrode lead ineach tube extending from said cup portion to the region where therespective tubes join the container, sealing material in said cupportions surrounding said electrode leads and a quantity of indium insaid container to facilitate passage oi. an electric potential from onelead to the other.

2. A source of ultra violet light comprising an elongated container, ahollow tube portion on each side of the midsection and leadingdownwardly therefrom and reversed upon itself to lead upwardly andterminating in an upwardly opening cup portion, an electrode lead ineach tube extending from said cup portion to the region where therespective tubes join the container, sealing material in said cupportions surrounding said electrode leads and a quantity of indium insaid container to facilitate passage of an electric potential from onelead to the other,

3. A gaseous discharge device comprising a crescent shaped containerwith its bottom portion arched upwardly adjacent the midsection, ahollow tube portion on each side of the midsection and leadingdownwardly therefrom and reversed upon itself to lead upwardly andterminating in an upwardly opening cup portion, an electrode lead ineach tube extending from said cup portion to the region where therespective tubes join the container, sealing material in said cupportions surrounding said electrode leads and a quantity of vaporimblemetal in said container to facilitate passage of an electric potentialfrom one lead to the other.

4. A gaseous discharge device comprising an elongated container, ahollow tube portion on each side 0! the mldsection and leadingdownwardly therefrom and reversed upon itself to lead upwardly andterminating in an upwardly openin: cup portion, an electrode lead ineach tube extending from said cup portion to the region where therespective tubes join the container, sealing material in said cupportions surrounding said electrode leads and a quantity of vaporizablemetal in said container to facilitate passage of an electric potentialfrom one lead to the other.

JOHN A. HANNUM.

